scienceofdoom.com

I would like to refer CA readers to an excellent and relatively new blog scienceofdoom.com. Its policies commit it to a couple of things that are important departures from realclimate, climateprogress and similar sites, which spend much of their energy persecuting infidels, agnostics and perceived heretics on even minor creeds, the latter attracting particular venom.

According to its policies, it is committed to treating the “public” (which, in the technical blogosphere, is very often highly educated scientists and professionals from other fields) with respect, even if they ask heretical questions, rather than treating them as “part of an evil empire of disinformation”. It is committed to questions like: “What is this particular theory built on? How long has theory been “established”? What lines of evidence support this theory?”. These are obviously the sort of questions that are regularly addressed at Climate Audit in respect to proxies – and ones that I would have liked to be able to address in the physics if I could clone myself so that I had more time and energy.

SDoom commenced its life with many useful posts outlining the fundamentals of sensitivity of CO2, drawing heavily on Ramanathan’s work on radiative-convective models in the 1970s. (They describe him as the “great Ramanathan”.) In a few CA posts, I’ve drawn readers attention to Ramanathan’s articles on radiative-convective models, expressing my considerable frustration at IPCC’s failure to properly present a canonical and approved version of the fundamentals, embodying any advances since Ramanathan. My own sense – a view previously expressed at CA – is that in order to provide the appropriate food for a scientist from another field, there is a pressing and long overdue need for exposition somewhere between a primary school cartoon and merely reporting the results of GCM runs, meritorious as they may be. I suggested this long ago to one of the scopers of AR4 and it is something that the scopers of AR5 need to consider. My guess is that an exposition building on radiative-convective models a la Ramanathan would be the most fruitful way of accomplishing this. SD’s fresh presentations of Ramanathan’s work should be of considerable interest to people trying to understand the larger problem.

Their statement of objectives very much represents my view of the world – despite the efforts of opponents to paint me otherwise. Their emphasis on politeness is very much along the lines of what I try to do here. I try to be polite personally; I ask commenters here to be polite and have spent a considerable amount of time enforcing politeness rules. SDoom note that they may “use satire now and again as it can make the day more interesting” – something that I also do. From personal experience, I’d advise SDoom that it’s a voice that one has to watch as it requires a pretty deft touch to pull off successfully and won’t always give the intended results. On the other hand, satire and a light touch are far more agreeable than the angriness that one sees all too often in the blogosphere.

I quote their policies in full below:

What’s the blog about?
Climate science.

Who’s it for?
People interested in the science behind the climate stories we read about every day. People who want to learn. People who want to contribute to other people learning about climate science.

What does the author think about Science?
Science is not a religion. It’s good to ask questions. Being skeptical is a positive thing. When people of an alternative viewpoint use catchy but insulting labels for you, keep asking questions and thinking for yourself. Science isn’t settled by being able to come up with the best insults, although it can be a lot of fun – even for grown ups.

What does the author think about Climate Science?
It’s a fascinating subject and something really worth trying to understand.

A little more specific?
Some aspects of current “Climate Science” have become more like a faith. The science has been pressed into a political agenda and consequently the spirit of free inquiry has been squashed.

Opinions
Opinions are often interesting and sometimes entertaining. But what do we learn from opinions? It’s more useful to understand the science behind the subject. What is this particular theory built on? How long has theory been “established”? What lines of evidence support this theory? What evidence would falsify this theory? What do opposing theories say?

Anything else?
This blog will try and stay away from guessing motives and insulting people because of how they vote or their religious beliefs. However, this doesn’t mean we won’t use satire now and again as it can make the day more interesting.

Comments and Questions
These are encouraged. But check out the etiquette. Otherwise the spam filter may eat your comments for breakfast. If not, the moderator will lunch on them.

A Calmer World
It’s easy to trade blows on blogs. It’s harder to understand a new point of view. Or to consider that a different point of view might be right. And yet, more constructive for everyone if we take a moment, a day even, and try and really understand that other point of view. Even if it’s still wrong, we are better off for making the effort.

And sometimes others put forward points of view or “facts” that are obviously wrong and easily refuted. Pretend for a moment that they aren’t part of an evil empire of disinformation and think how best to explain the error in an inoffensive way.

So many blogs out there that it’s getting to be a cacophony. But goods ones are always welcome.
On politeness:

…important departures from realclimate, climateprogress and similar sites, which spend much of their energy persecuting infidels, agnostics and perceived heretics on even minor creeds, the latter attracting particular venom.

Yes, sometimes we have to find creative ways of calling a spade a spade, and not just say it directly.

“My own sense – a view previously expressed at CA – is that in order to provide the appropriate food for a scientist from another field, there is a pressing and long overdue need for exposition somewhere between a primary school cartoon and merely reporting the results of GCM runs, meritorious as they may be.”

There are numbers of textbooks which do just that, as well as numbers of university courses.

Steve: Introductory material is summarized in many authoritatitive reports. That would have been far more useful in AR4 than its self-congratulaory history of climate science – histories are also covered in textbooks and university courses. I don’t think that it’s a reasonable answer to tell a scientist from another field to go take a university course if he wants to understand the salient issues in climate science. I think that IPCC should be making every effort to convey that to the public. I also think that the assessment reports have ended up being a bit of a shout out to all the climate scientists who want their name in the IPCC, rather at the expense of providing useful information to policy makers. This is at least partly due to the terms of reference of IPCC assessment reports – a matter that should be reflected on by IPCC officials.

“I don’t think that it’s a reasonable answer to tell a scientist from another field to go take a university course if he wants to understand the salient issues in climate science.” — your choice, you can learn from textbooks if you want, it will just take longer.

At least on your web site I have learned something over the years. If i wanted to discuss Science Fiction or science fantasy I would visit a blog associated with that. The visit to SOD was a let down after reading your intro!

Steve- it’s just a blog; it’s not the Ten Commandments. But he says that he’s trying to be respectful. Don’t you think that that deserves encouragement – relative to peoplae like Tamino, Tim Lambert, Eli Rabett and Gavin Schmidt? Maybe he won’t live up to his policies – but then readers can hold him to account and my guess is that anyone who sets out policies of respectfulness will try to live up to them. We’ll see.

Steve: Lindzen doesn’t contest the first-order CO2 effect. The downwelling spectra are things that I think IPCC should have shown to deal with the “just a trace gas” argument. The $64 issue comes with clouds and feedback and it will be interesting to see how that goes. This has been the big question since Charney. In my opinion, IPCC should have very large sections, even chapters, on the most important scientific issue, rather than the relatively thin gruel that AR4 offered.

An excellent site – recommended!!!!.
It would be good to see anyone who KNOWS the science of climate to visit the site and help out on questions posed by commenters, and to correct, or demonstratably agree with the owner’s science.
This way it could become an excellent resource of the science as she is known today.

I hope scienceofdoom will not mind if I repost a question I posed there over here!
———————————————
A question!

A molecule absorbs a photon
It is now more energetic/warmer – is this causing it to vibrate or have electrons jumped a level?
If vibration; then energy can be shared with other molecules. If this is the case then doesn’t re-radiation occur at longer and longer wavelengths as the blackbody temperature has been reduced by the sharing of energy?
If electrons have jumped then their return should emit a photon of the same wavelength – no energy loss? This will be emitted in any direction at random. Is it true to assume that further collisions will occur to those emitted in directions close to the horizontal until after enough collissions 50% go up and 50% go down (on a disc world)?
If it is not a flat earth then a larger proportion of the horizontal photons will go up to space is this correct?

Re: UK John (May 2 14:52),
Perhaps this should be posted at scienceofdoom’s blog but I will take a stab at your questions simply to test my own understanding.

A molecule absorbs a photonI assume we are talking about a long wave photon and the so called greenhouse gas, CO2.

It is now more energetic/warmer – is this causing it to vibrate or have electrons jumped a level?At infrared photon energies, the absorption is to to quantized changes in molecular vibration states.

If vibration; then energy can be shared with other molecules. If this is the case then doesn’t re-radiation occur at longer and longer wavelengths as the blackbody temperature has been reduced by the sharing of energy?Sort of correct. In dense gases like in our troposphere, the mean time between molecular collisions is much less than the time that the molecule remains excited and the predominant collisions cause the energy to be thermalized rather than re emitted at the original photon energy. The warmed dense gas has a thermal spectrum and radiates in all directions with only a small part of the energy radiated at the absorption wavelengths of CO2. Thus, one can see how the energy emitted in the absorption bands of CO2 gets quickly spread over a broad thermal spectrum and conceptually explains the theoretical diminishing logarithmic effect of increasing concentrations of CO2 in the atmosphere.

If electrons have jumped then their return should emit a photon of the same wavelength – no energy loss? This will be emitted in any direction at random. Is it true to assume that further collisions will occur to those emitted in directions close to the horizontal until after enough collissions 50% go up and 50% go down (on a disc world)?
If it is not a flat earth then a larger proportion of the horizontal photons will go up to space is this correct?There would be more re emmission events in the stratosphere where the gas density is much lower. (The earth subtends substantially less than half the radiative sphere also). There is also much less water vapour present. I really out of my element in figuring out the role of stratospheric greenhouse gases, but then again, I haven’t seen anything definitive on it.

Me, I kind of go along with the 1.2K for doubling first order effect. Then you throw in the clouds and other wild cards and who knows which way is up or down?

I have never commented on this blog before, but I read it often. Typically the statistical posts are over my head, but in the case of IR absorption I am much more learned. When a molecule absorbs IR radiation, it absorbs it through vibrational modes. In a gas, the molecule also is influenced by rotation, so vibrational modes are absorbed with rotational influence (perturbation). This is most classically taught with the vibrational/rotational spectrum of HCl gas and can be found in most P-Chem text books. Not all molecules absorb IR radiation, in fact only molecules that have a permanent dipole moment are able to absorb radiation. This is why N2 and O2 and other elemental diatoms are not absorbers of IR radiation while H20 and CO2 are. To further complicate the matter, the symmetry of the molecule accounts for what types of vibrational modes are able to absorb radiation. The more symmetric the molecule, in general, the fewer the vibrational modes it can absorb. The absorption of IR radiation has to do with the vibration being in resonance with the radiation frequency. When a light frequency is in resonance with a vibrational mode, the vibrational mode is excited. But as soon as the radiation is absorbed, it is released. Unless the radiation is continuous, the vibrational mode will immediately fall back to its ground state. The easiest model used to calculate vibrational energy absorption is the harmonic oscillator. The harmonic oscillator model uses the masses of the two atoms and the bond strength between them (akin to how tight of a rubber band is between them) and calculates the kinetic energy of the vibration. This is a classical physics model, which is a simplified model since we are dealing with quantum physics. Quantum calculations begin to take into account perturbation from other vibrational and rotational modes, blah blah blah.

Despite all this, I am not sure how such small quanta of energy can actually add up to a measurable warmth from radiation causing molecular vibrations to absorb (and released) the energy. To date I am not aware of any experiment performed in which a measurable temperature change (increase) was made due to IR absorption of a gas. The green house effect is often bandied about, but I have yet to read a definitive thermodynamic explanation of how it works.

My understanding is when the energy is reemitted it goes in a random direction. What this means is some of the upward moving IR radiation is reflected back to the ground which reduces the rate of cooling during the night. This causes the atmosphere temperature to rise until it reaches a new equilibirum point that depends on the amount of energy being reflected which, in turn, depends on the concentration of GHGs.

it is not so simple. First at all, only the divergence of the radiative flux at a given point within the atmosphere is relevant, but not the magnitude of the flux. What the divergence means can be described as follows:

If there is a thin layer of air of the thickness dz and the radiative flux R is changed during the transfer across this layer by the amount of dR, the divergence can be expressed by dR/dz.

The radiative flux, of course, is a vector. Thus, we have to consider the change of R not only in the vertical direction Z, but also in the horizontal directions X and Y, expressed by div R = dR/dx + dR/dy + dR/dz. Obviously, the divergence of a vector is a scalar.

However, the divergence of the radiative flux contributes to a change of internal energy with respect to time. There is a conservation equation for internal energy, but not for temperature. A prognostic equation for the temperature can be derived from the conservation equation for internal energy (alternatively the conservation equation for enthalpy) using some assumptions. One of them is the assumption of the local thermodynamic equilibrium. Even in this prognostic equation the divergence of the radiative flux occurs.

If we ignore for a moment all other energy fluxes and heat effects and only consider the change of R in the vertical direction, the resulting equation reads (e.g., Collins et al., 2006, eq. (1)):

rho c_p dT/dt = – dR/dz

Here, rho is the density of air, c_p the specific heat of air at constant pressure, T is the abs. temperature of air, and t is time.

CO_2 molecules have no permanent dipole moment. Therefore, they have only vibrational modes (symmetric and anti-symmetric stretches, ny_1 and ny_3, bending motion, ny_2). The bending mode consists of two vibrations at the same frequency. According to Liou (2002) and others, the perpendicular vibration is coupled with rotational transitions corresponding to changes in the quantum number by +1 (R branch), 0 (Q branch), -1 (P branch). The bending mode is related to the 15 my fundamental. The vibration mode ny_1 is radiatively inactive at its fundamental, while the mode ny_3 is related to the 4.3 my fundamental.

You are correct. After looking back at what I wrote, rotational absorptions require a permenant dipole moment. Vibrational modes require the dipole moment of the molecule to change during a vibration. Heteronuclear diatomic molecules are therefore active, while homonuclear diatomics are not active, their dipole moment remains 0 during a vibration.

The CO2 molecule is a linear molecule, as such it is quite symmetric and vibrational motions only corresponding to dipole moment changes can be active. The symmetric stretching mode has no change in dipole moment and therefore is IR inactive while the anti-symmetric stretch is active since the dipole moment changes. Both bending modes are IR active.

The more atoms in a molecule, the more complex the selection rules for IR activity can become. Symmetry and Group Theory are then used to determine what normal modes (fundementals) will be active in the IR frequency range, as I am sure you already know.

There was a classic experiment conducted by Tyndall and Bell about 1880. They made a chamber with a rubber diaphragm and an IR transparent window. They filled the chamber with an IR absorbing gas and exposed the chamber to an IR beam. When they interrupted the IR beam at a sonic frequency they could hear the sound generated by the expanding and contracting gas. There are commercial IR gas analyzers that use this detection principle.

@thefordprefect — When a photon is absorbed by an atom, part of the energy may go into causing an electron to jump up a level and the rest into increased vibration. When the electron drops back to its ground state, the photon radiated is of lower energy and longer wavelength.

There’s also a phenomenon known in the semiconductor arena as “indirect bandgap”, in which an absorbed photon causes electrons to jump up two (or more) levels. When the electron drops back one level, it emits a lower-energy, longer-wavelength photon. A second lower-energy, longer wavelength photon is emitted when the electron drops back to the ground state.

I discovered Science of Doom a week or two ago and have found its articles generally interesting and informative – definitely recommended. And it is helpful in pointing out important physical science papers to readers (such as two by Ramanathan).

For a (quite lengthy, detailed and moderately mathematical) primer on atmospheric science, I recommend the Lecture notes on Physical Meteorology by Rodrigo Caballero of University College Dublin, downloadeable at http://mathsci.ucd.ie/met/msc/PhysMet/PhysMetLectNotes.pdf. One of the many subjects it covers in detail is the mechanisms of absorption of photons, giving rise to vibrational and rotational energy, and the thermalization of that energy by repeated collisions prior to emission of another photon (typically of lower energy than the one absorbed).

I was at the local B&N just now, and I looked around for a ‘decent climate science book’, focused on the science. All I could find was alarmist books from James Hansen, Stephen Schneider and James Hoggan etc. There were books by Pat Michaels, Christopher Horner and a few other wind-power pushers. Bjorn Lomborg’s ‘The Skeptical Environmentalist’ looked scholarly, but had too much on the environment, not just climate science. Al Gore has a book for kids where he explains how the smart grid will be a great thing to have.

In one part of Hansen’s book I caught when I flipped through, he writes about his car journey where he suddenly comes up on a deer on the highway, cannot control his car quickly enough and ends up running it over. The deer dies. Hansen writes on how he

…”burst into tears. I did not know whether I was crying for myself, the deer, or the planet”.

Moving stuff indeed.

I came back empty-handed.

The same phenomenon repeats itself in the evolution/biology section. It is chock-full of books ranting against creationism and ‘design’. Where are the books that simply teach you Darvwinian evolution?

Infrared/microwave radiation absorption causes the molecule to vibrate. The photons at those wavelenghts are not energetic enough to cause electrons to jump ‘orbits’.

You cannot think just about the single molecule / photon but the whole gas / radiation: the gas absorbs the radiation, increase its temperature and re-emits radiation – ‘cooling’ by transferring heat (vibration) to ‘other’ molecules does not happen – ALL the molecules are absorbing…(on average).

You are right that 50% goes ‘up’ and 50% ‘down’ – but the 50% that goes back towards the ground would not have happened if the gas was not there..it is a gain.

I appreciate Science of Doom for the educational material he presents. I’ve found it very stiumlating and I may be less ignorant now than before I visited as a result.
There is scholarship there. He is not inflamed by questions, he addresses them thoughtfully.

The paper of Ramanathan and Coakley (1978) is a typical examples of playing with numerical models. First at all, Eq. (6) of that paper is incomplete and incorrect. This equation does not contain the individual derivation of the air pressure with respect to time, it also does not contain heat effects due to phase transition processes. According to the definition of the term Q, terms of this equation have different physical units.

The authors obtained results strongly depending on the authors’ assumptions. If these assumptions are not fulfilled the results are of minor importance.

Nevertheless, I like the Table 2 of that paper considered for the northern hemisphere. Following this table the atmosphere is cooling due to the loss of 168 W/m^2 by infrared (long-wave) radiation. The earth’s surface is cooling due to the loss of 60 W/m^2 by infrared radiation, too. Only solar radiation contributes to the heating of the earth’s surface (correctly spoken in the layer of the earth adjacent to its surface; 165 W/m^2) and the atmosphere (63 W/m^2).

In 1971, Professor Dr. habil. Heinz Fortak, the Director of the Institute for Theoretical Meteorology at the Free University of Berlin, Germany, argued in his book “Meteorologie”:

The “cycle” of the long-wave radiation between that Earth’s surface and the atmosphere does not contribute to the heating of the system. The outgoing emission of infrared radiation only serves to maintain the radiative equilibrium at the top of the atmosphere.

As argued by Fortak, and eventually documented by many considerations on the global energy budget of the system Earth-atmosphere there is no space for the so-called atmospheric greenhouse effect.

Thank you, very helpful.
I am still struggling with a number of issues like:
Exactly how (why) does the greenhouse effect work?
Is methane really a powerful ghg, considering it absorbs radiation in much the same spectra as water vapor?
How much faster are day to night-temperature dropping due to global warming?
–
Maybe I will find the answers…or not.

I second the recommendation for Caballero’s on line lecture notes. It’s a work in progress and has been expanded considerably since I discovered it a year or two ago. I’m looking forward to his expansion of the section on convection in the planetary boundary layer. Note that there are some peculiarities in how meteorologists treat entropy, but it’s not any worse than the difference between chemists and physicists on thermodynamics where chemists prefer constant pressure and physicists constant volume.

My criticism (positive I hope) is that the site is a centre for presenting current climate science and it does that very well. What it lacks to a small part is response to some hard physics questions. These tend to be elided or avoided.

I’d be interested to see a first rate physicist contribute to the dialog. Either as an author or as a commenter. I’d suggest Lubos Motl for a start, but I realise that may be problematic with the neutral POV so far presented.

SoD is doing a very good job. Clearly far in advance of most of our limited knowledge. It would help all of us if the same tenor progressed, but that edited guest posts were included to flesh out the parts that SoD was hesitant to comment on (he is a reporter after all)

I should point out that SoD does a very good job of answering most questions.

My only complaint is that questions ‘out of scope’ get a little bit lost. Unfortunately these are usually esoteric physics questions that are relevant but ‘difficult’. Hence I suggest that guests are included to respond to specific questions.

My problem with the purely irradiative model is that it doesn’t explain the actual heat transfer from the surface into the atmosphere. The overwhelming mechanism for this is the evaporation of water and its condensation at altitude. Because of the hydrogen bonding in water in all 3 main phases it is capable of transferring enormous amounts of energy. The latent heat of vaporization is approximately 600 calories per gram. This energy is transported aloft in the form of fast moving water molecules mixed among the air molecules. The concentration of water can be as high as 4 percent. CO2 molecules carry less than 1 calorie per gram aloft. Their concentration is 0.038 percent.

The heat transfer effect of water is thus 10,000’s of times greater than that of CO2.

I’m sorry, but I only see 600 Cal/gram transferred to water molecules at the surface causing them to enter the gaseous atmosphere. From that point on, the high energy (translational and vibrational) will be transferred to slower air molecules eventually arriving at a homogeneous translational energy (heat as shown by temperature). At some point (the dew point) the now less energetic water molecules will begin to associate to form water and fall through the atmosphere back to the surface.

The net result must be a substantial transfer of translational energy to the larger volume of air. The total budget invoves the transfer of surface heat to the atmosphere above during the daylight hours and a general reversal at night.

Many thx to Bill MacLean to remember us that earth is not a simple “irradiative model” as assesses to many times in scienceofdoom.com.
Now that AGW is facing serious problem with its linear view on earth climate, we don’t need any non linear proxy hypothesis to demonstrate falsification. Never forget that behind that you still have a poor balloon sent by Boulder and few data always filtered by tons and tons of “honest points of view”.

Thank You Steve, for describing and providing a link to this useful site.

[OT, Continuing from Ford Prefect’s question:

When a photon of the right frequency encounters a CO2 molecule, it MIGHT be absorbed by the molecule and the energy used as to power a vibration mode. (The probability of this happening is frequency dependant).

The molecule will tend to relax to its non-vibrating state very quickly (Probability 1-1/e in about 10^-5 sec) but it is MUCH more likely that the molecule will collide with another molecule (average collision rate at STP is about 10^10 per sec) before it can do that, and the energy will be converted from vibration to Kinetic Energy. So practically all absorbed radiation goes into heating up the gaseous ensemble.

At the same time collisions of unexcited CO2 molecules sometimes result in vibrations which can result (by the unlikely process above) in radiation of a photon.

[i]The molecule will tend to relax to its non-vibrating state very quickly (Probability 1-1/e in about 10^-5 sec) but it is MUCH more likely that the molecule will collide with another molecule (average collision rate at STP is about 10^10 per sec) before it can do that, and the energy will be converted from vibration to Kinetic Energy. So practically all absorbed radiation goes into heating up the gaseous ensemble.[/i]

This part is completely wrong and yet the same error is done all the time .
Yes absorbed radiation may transform in kinetic energy by collisions .
But what about the [b]REVERSE[/b] process ?
Of course it is well known that everything that is microscopically possible in one direction of time is also possible in the other direction of time.
In equilibrium it’s even more specific : the (+t) process has the same probability as the (-t) process .
So from these well known facts follows that the absorbing molecule will give away exactly as much vibrationnal energy by collisons as it will receive by collisions.
So it is not true that CO2 “heats” other gases by collisions .
It both heats and cools them in equal amounts .
There can be no net energy transfer between CO2 and the other gases in equilibrium.
Whether a gaz absorbs IR photons or not is completely irrelevant to the basic principle that 1 molecular species can’t “heat” (or “cool”) another species in equilibrium .

There can be no net energy transfer between CO2 and the other gases in equilibrium.

But as you have frequently pointed out, there is no equilibrium. Energy is continually lost to space and supplied from above and below by radiation and convection and by absorption of incoming solar radiation. So are you saying that in the absence on an outside energy source, the atmosphere would not cool by radiation to space?

I’m really surprised, Tom, that you’ve made such a logical error as to say,

So it is not true that CO2 “heats” other gases by collisions .

Though your individual statements are correct, you then go on to say

Whether a gaz absorbs IR photons or not is completely irrelevant

It’s entirely relevant when it comes to talking about CO2 heating other gases. The CO2 absorbs IR and thus becomes “hotter” in terms of total energy. The vibrational excess is then given up to other gasses (O2 and N2 primarily, but even H2O). If the CO2 wasn’t present or was present in smaller quantities, the amount of this energy transfer would be less. The energy that the CO2 absorbs by collision is related to the temperature of the surrounding gas, but the amount given up by CO2 is augmented by he amount of IR absorbed and this will generally be greater than the amount of IR emitted unless the surface below is cooler than the gas parcel in question.

but the amount given up by CO2 is augmented by he amount of IR absorbed and this will generally be greater than the amount of IR emitted unless the surface below is cooler than the gas parcel in question.

The amount emitted by ghg’s will always be greater than or equal to the amount absorbed in the thermal IR at constant temperature. If there is excess absorption, the temperature will increase, increasing the emission and conversely. Energy also comes in by convection from the surface and from near IR absorption of incoming sunlight. The emissivity and absorptivity are equal for LTE conditions, but not the emission and absorption.

Yep, and that doesn’t include the details concerning how much various frequencies are saturated with respect to the surface. Thus if a particular frequency is 99.9 absorbed before it reaches our particular parcel, then there will only about .1% of an excess in the amount of IR in that frequency which enters the parcel compared with what the amount which would be expected given the temperature of the atmosphere below it. OTOH if a frequency was only 2% saturated, then there’d be almost double the amount of IR in the IR reaching our parcel.

Which brings me to a question I asked myself when composing the previous comment. I tried to avoid making an assumption of the answer until someone could reply to it. Given that the surface emits IR in a continuum while the atmosphere only absorbs / emits at frequencies characteristic of the GHGs in it, and given that the surface is denser than the atmosphere, how does this play out in terms of the actual number if IR photons emitted by the surface and atmosphere at a given frequency [band / width] respectively? If the surface and a given parcel of atmosphere were at the same temperature, does knowing the emissivity of the surface and say CO2 at a wavelength where only CO2 emits to any great extent let you calculate the emission directly?

Stupid form isn’t remembering my name and email address like it used to.

Thus if a particular frequency is 99.9 absorbed before it reaches our particular parcel, then there will only about .1% of an excess in the amount of IR in that frequency which enters the parcel compared with what the amount which would be expected given the temperature of the atmosphere below it. OTOH if a frequency was only 2% saturated, then there’d be almost double the amount of IR in the IR reaching our parcel.

That’s only true if the emissivity of the gas at the frequency of the incident radiation is vanishingly small. The classic example is O2/O3 absorbing in the UV. Once the UV has been absorbed there is no more. In the thermal IR, however, saturation means the absorptivity is effectively 1, which means the emissivity is also 1 (Kirchoff’s Law). So the answer to your question is yes, the emission intensity is controlled only by the value of the Planck function for the temperature and wavelength (frequency). So a parcel of air at the same temperature as the surface emits just as much as the surface at a saturated wavelength, possibly more if the surface has an emissivity less than 1, both upwards and downwards. That’s the principle behind both band and line-by-line radiative transfer models. You calculate the optical depth, which is a function of number density per unit volume for every line of every molecule for whatever spectral resolution you are using in your model, convert the optical depth to emissivity and multiply it by the Planck function.

An isothermal atmosphere would not have a greenhouse effect because emission at the top of the atmosphere would be exactly the same as at the surface. However, a radiative isothermal atmosphere is not stable because the top slab of the atmosphere is emitting twice as much radiation as it’s absorbing and would cool rapidly. The characteristics of our atmosphere are such that if you could freeze the atmosphere in place and completely prevent convection, the lapse rate would be about 16 degrees/km and the surface temperature would be higher. But that’s higher than even the dry adiabatic lapse rate and so convection forces the actual lapse rate to a lower value and results in significant heat transfer from the surface and a lower surface temperature. With a temperature gradient and a saturated line, emission from the top of the atmosphere up is less than the emission from the bottom down and you do get a greenhouse effect.

Stupid form isn’t remembering my name and email address like it used to.

I’ve been having the same problem the past week or two. Don’t know what the problem is. An “upgrade” of either Firefox or Windows or WordPress, I suppose.

That’s only true if the emissivity of the gas at the frequency of the incident radiation is vanishingly small.

I’m not sure what you mean there. As was pointed out by Colin above, in the lower troposphere, the chance of thermalization is thousands of times more likely than emission, so having a CO2 molecule with the right energy to emit at a given frequency is almost always going to be as a result of a collision rather than as a result of absorbing a photon of that frequency.

In the thermal IR, however, saturation means the absorptivity is effectively 1

Again I don’t understand you. Say we’re talking about 1 kilometer up in the atmosphere. The chance that a given photon of IR emitted from the surface with a frequency reasonably close to a CO2 line (and one not close to an H2O band) will make it that high will depend on the temperature, concentration of CO2 and emissivity at that frequency (and of course, lots of other details, we don’t need to get into.) If we assume the frequency is pretty unsaturated, then at 1km it will consist of a lot of photons emitted by the surface which haven’t been absorbed plus some photons emitted upward from every level of the atmosphere in accordance with the temperature at that level. Hmmm. I guess I was wrong in saying the 2% emissivity line would have twice as much IR. I’d been thinking using a 50% line but decided it was too confusing a number to use and switched it without thinking things through. The point I was trying to make was that the extra IR emitted by the surface which doesn’t get absorbed will be like a additive term to the amount emitted by GHGs which also escape.

Lets assume you had a calibrated IR emission spectrophotometer tuned to the 15 micrometer line. If you point it at a blackbody at any temperature, the observed emission intensity will be the intensity calculated by the Planck function. Now let’s point it at cell containing pure CO2 at 1013 mbar at a controlled temperature. Assume the cell windows are perfectly transparent so they contribute nothing to the emitted intensity. If the cell is long enough so that 99.9 % of IR radiation at 15 micrometers would be absorbed if you tried to pass it through the cell, what intensity would you measure if there were no light source at the other end of the cell? The answer is that you would measure 99.9% of the intensity emitted by a black body. In an IR absorption spectrophotometer, the light source has a much higher temperature than 300K, more like 1200K, so the intensity is much, much higher than for a 300K blackbody and the sample emission can usually be ignored. You can also modulate the incident beam with a chopper and use a phase locked detector to discriminate against the constant sample emission.

The fact that inelastic collisions greatly outnumber radiative emission is actually required for Kirchhoff’s Law to be valid. But that doesn’t mean there isn’t any emission. You can use the Boltzmann distribution to calculate the fraction of molecules in an excited state based on the energy of the state, the temperature and the degeneracy (number of equivalent modes). For the 15 micrometer line at 300 K and any reasonable pressure, there are two equivalent modes and about 7% of all CO2 molecules will be in the excited state at any given time. Some of these will emit, even though most of them will not.

Or to put it yet another way: Just because 99.9% of photons emitted from the surface are absorbed for a given path length does not mean that the observed intensity of photons at the end of the path is 0.1% of that emitted by the surface. It depends on the temperature and wavelength. The value of the Planck function for UV emission from a black body at 300K is vanishingly small. But it’s not small for 15 micrometers at 300K. The difference between a blackbody and a gas is that the emissivity/absorptivity varies a lot with wavelength for a gas, but the maximum intensity can never be higher than what’s emitted by a blackbody at that temperature and wavelength. The emission spectrum of a gas is then the product of the emissivity and the Planck function at the wavelength and temperature of interest. Kirchhoff’s Law is that for a gas in local thermal equilibrium, emissivity is exactly equal to absorptivity.

Does not the following statement violate the Second Law of Thermodynamics?

“Of course it is well known that everything that is microscopically possible in one direction of time is also possible in the other direction of time. In equilibrium it’s even more specific : the (+t) process has the same probability as the (-t) process .”

Does not the following statement violate the Second Law of Thermodynamics?

Not really. It’s about details, not rates. For example, If you look at a diagram of a positron colliding with an electron to produce a gamma ray, it looks exactly the same as the diagram of a gamma ray producing an electron-positron pair except the directions are reversed. Microscopic reversibility is required by the First Law (Conservation of Energy).

The Second Law is all about bulk properties. While the probability of the reverse and forward reaction at equilibrium is the same, the probability that all reactions will run in the same direction at the same time is vanishingly small. Think of coin flips with 10^23 coins. What’s the probability that they will all come up heads at the same time?

“I would prefer that people discuss this sort of issue at scienceofdoom or elsewhere. I’m not really interested in bandwidth here being spent on very basic issues of infrared radiation and absorption and don’t wish to moderate the discussion. These are interesting issues and worth studying but better to do at a blog that’s covering this sort of thing.”

Dewitt,
It is a useful explanation. I do not think that it is understood that 1) molecules at a temperature > 0K act as blackbodies, 2) gases at a temperature also act as blackbodies (or greybody – maybe its the term body) of that temperature, and 2) therefore, the various levels of the atmosphere (gaseous bodies) do likewise.

Not realizing that a gas that can absorb radiation must also emit seems to be a common problem. The other big one is net heat flow versus gross heat flow. Look at the comments on Willis Eschenbach’s Steel Greenhouse post at WUWT. It’s depressing. It almost makes one want to be a warmer. Reading the comments at RC, however, will cure that problem. Both sites would benefit from a Zamboni of all piling on and OT comments.

On further consideration, my detailed reply sucks. I’ve never been all that good at explaining things. I recommend reading

Well, my last message wasn’t the greatest either, but I posted it just because I’d put too much time into trying to get my point across to just junk it. Anyway, what were you hoping I’d learn from the reference? I scanned the first 10-15 pages starting where you point and didn’t see anything I didn’t know already (I did get an A in Physical Chemistry; though it was 40 years ago.) I’m not denying I’m sometimes not able to state clearly what I know, but I think this discussion is lacking in explicit statements of what exactly is at issue. And that may be mostly my fault. If I find time today, I’ll try posting what I think needs to be discussed.

I would prefer that people discuss this sort of issue at scienceofdoom or elsewhere. I’m not really interested in bandwidth here being spent on very basic issues of infrared radiation and absorption and don’t wish to moderate the discussion. These are interesting issues and worth studying but better to do at a blog that’s covering this sort of thing.

I second Dave’s comments, more or less. It’s the technical stuff that interests me the most. I’m a little surprised you didn’t get into the unit root discussion, for example, as that is statistics and originated in econometrics. As far as moderation, keeping the discussion civil, on-topic and no piling on would be all that’s needed. I say that without having any idea of how much work that would actually be. Of course, your house, your rules.

Steve: Just a quick thanks for the link. As your site is related to stats, I’ve been loath to press too hard for some review of stuff I’ve been working on. Science of doom is an excellent site. I’m afraid that whomever it is that is replying to me at SoD may end up converting me to the AGW school. Then again, I may accomplish the opposite. Nice to be part of an exchange that is rooted in verifiable facts!

It is the most informative site I’ve found to date on CO2 science. Thanks again for the pointer.

Is Climate Science experimental at all? Are there reports of relatively recent experiments which have caused some interesting debates in the field? Or looking more to the past, have there been hypotheses in Climate Science that have been falsifed through experiment?

Yes. Experimentation has been quite extensively used and quoted in the literature, particularly with respect to the items explained on scienceofdoom. Go there. Read. Learn.

Yes. A global experiment on aerosols is currently underway. Also, see CFC’s. Both experiments seem to be supporting the original hypothesis. For the most part, the science of “climate science” is relatively simple and not ground breaking. Highly unlikely to find recent experiments causing interesting debates in such a field.

I have no information confirming or contradicting that question. Personally, I believe I can show that at levels above 200 ppm, CO2 no longer impacts on climate. I am in the process of determining if the good folk at scienceofdoom can falsify this. You should visit there. Great site. VERY educational.

Cheers

JE (not in any way associated with science of doom, or climate audit, other than as an acolyte)

I’m not really interested in bandwidth here being spent on very basic issues of infrared radiation and absorption and don’t wish to moderate the discussion.

I note your message was still on the Recent Comments list when I started this message, so I decided to comment (actually I did yesterday, but had forgot to enter name and e-mail which doesn’t happen automatically on this site anymore for whataver reason). So the question is what has happened to your bandwidth lately? I think the answer is clearly that you’ve not been posting many scientifically interesting posts, so you don’t get many comments. You don’t like politics to be discussed here, and when you’ve tried it yourself, as in the recent posts, you got so much blow-back that you had to pull a RC and shut off the comments. And while it’s somewhat interesting to dig through the ClimateGate e-mails, they’ve mostly been done to death and few are interested in commenting except concerning politics or personal analysis.

Since both DeWitt and I were being polite to each other, I assume you mean by “moderate” that you feel you’d have to comment on the subject itself and don’t want to. Fair enough, but if you don’t have people commenting regularly in an interesting way, pretty soon you’ll be a 2nd tier science blog. I note you’ve slipped to 7th this morning on the top science blogs, as low as I’ve ever seen you. I don’t want to be a TCO, but you might want to think about getting back to your roots.

I read most o the various AGW blogs, and id have to disagree;-) It dosnt take a terribly objective person to see what angle that site is shooting from. There is a weeee bit o faith involved in some o the “skeptical” conclusions drawn. Im a fan of the Science Of Doom. Just because it does deal with the “facts” as they are known, and he states the areas of uncertainty.

Dont get me wrong, they have interesting discussions at Skeptical Science at times. But there is a difference between the two sites in how they “interpret/present” the “facts”.

Also been a long time fan of this site, but dont generally comment, as there are enough commentators that my queries are generally asked for me.

I am really looking hard for the proposed total forcing that CO2 is supposed to be having on the climate. I have found countless estimates for the forcing changes as CO2 increases, but not the total estimates.

If I reverse the dF = 5.35 ln(C/Co) and move the CO2 concentration into the ppb I get about -42 W/m2. This is not really what I need. A reference would be really helpful as well. I am guessing that the total amount of current forcing they will claim is 50-100 W/m2 (closer to 100). That fits with their models, but I simply cannot find it stated anywhere.

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[…] May 8, 2010 by scienceofdoom This post will suffer from the unfortunate effect of too much maths – something I try to avoid in most posts and certainly did in The Imaginary Second Law of Thermodynamics. It’s especially unfortunate as the blog has recent new found interest thanks to the very kind and unexpected words of Steve McIntyre of Climate Audit. […]